all characters became question marks. How to reverse that?

??? 2 ??? 1442 ?? ??? …. ?? ??? ?? ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? … ??? ??? ??? ??? ??? (??? ???) ?? ?? ??? ??? ??? (?? ???) ? ??? ?? ??? ??? ( ??? ??? ???/??? ??? ???).

This looks like a corrupt .odt file (i.e. the zip file is defect) (see comment of @mikekaganski ) You may want to upload your file to question but I doubt that anything can be recovered.

No way. You likely used a Text file format, and your encoding was unable to store the characters in your document; you likely had a warning about possible loss of information on save to such a format (unless you disabled such warnings at some point, which is equal to telling to the program “I know what I’m doing, don’t bother me with useful warnings that could save me from trouble!”). The data loss is irreversible.

No, it doesn’t look like a corrupt ZIP. It could be a case of a “New Word document” in Windows Explorer’s context menu, and as such would be tdf#123476 changed in 7.1 (with latest fixes targeted at 7.1.4).

Did this happen to some very old Microsoft Word document containing Cyrillic text?